In packaging technology, monitoring units with a test beam, particularly a photoelectric barrier, are required in many areas. These monitoring units have on the one hand the purpose of controlling the working procedures of the (packaging) machine, for example by means of print marks on material webs or blanks. On the other hand, however, precise positioning and/or formation of material webs also requires to be monitored.
The operation of the (packaging) machine is dependent on the correct functioning of the monitoring units. There in turn are sensitive to contamination, particularly to the dust and particle deposits which are unavoidable in packaging machines.
The object underlying the invention is to improve monitoring units of the type described in that they have an increased degree of operational reliability.